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Navigation Aids


−1−11. NAVAID Identifier Removal During


During periods of routine or emergency maintenance,
coded identification (or code and voice, where
applicable) is removed from certain FAA NAVAIDs.
Removal of identification serves as a warning to
pilots that the facility is officially off the air for

−up or repair and may be unreliable even though

intermittent or constant signals are received.


During periods of maintenance VHF ranges may radiate
a T

−E−S−T code (

D DDD -).


DO NOT attempt to fly a procedure that is NOTAMed out
of service even if the identification is present. In certain
cases, the identification may be transmitted for short
periods as part of the testing.


−1−12. NAVAIDs with Voice


Voice equipped en route radio navigational aids

are under the operational control of either a Flight
Service Station (FSS) or an approach control facility.
The voice communication is available on some
facilities. Hazardous Inflight Weather Advisory
Service (HIWAS) broadcast capability is available on
selected VOR sites throughout the conterminous U.S.
and does not provide two-way voice communication.
The availability of two-way voice communication
and HIWAS is indicated in the Chart Supplement
U.S. and aeronautical charts.


Unless otherwise noted on the chart, all radio

navigation aids operate continuously except during
shutdowns for maintenance. Hours of operation of
facilities not operating continuously are annotated on
charts and in the Chart Supplement U.S.


−1−13. User Reports Requested on

NAVAID or Global Navigation Satellite
System (GNSS) Performance or


Users of the National Airspace System (NAS)

can render valuable assistance in the early correction
of NAVAID malfunctions or GNSS problems and are
encouraged to report their observations of undesir-
able avionics performance. Although NAVAIDs are
monitored by electronic detectors, adverse effects of
electronic interference, new obstructions, or changes
in terrain near the NAVAID can exist without

detection by the ground monitors. Some of the
characteristics of malfunction or deteriorating
performance which should be reported are: erratic
course or bearing indications; intermittent, or full,
flag alarm; garbled, missing or obviously improper
coded identification; poor quality communications
reception; or, in the case of frequency interference, an
audible hum or tone accompanying radio communi-
cations or NAVAID identification. GNSS problems
are often characterized by navigation degradation or
service loss indications. For instance, pilots conduct-
ing operations in areas where there is GNSS
interference may be unable to use GPS for navigation,
and ADS

−B may be unavailable for surveillance.

Radio frequency interference may affect both
navigation for the pilot and surveillance by the air
traffic controller. Depending on the equipment and
integration, either an advisory light or message may
alert the pilot. Air traffic controllers monitoring

−B reports may stop receiving ADS−B position

messages and associated aircraft tracks.

In addition, malfunctioning, faulty, inappropriately
installed, operated, or modified GPS re


systems, intended to be used for aircraft maintenance
activities, have resulted in unintentional disruption
of aviation GNSS receivers. This type of disruption
could result in un

−flagged, erroneous position

information output to primary flight displays/indica-
tors and to other aircraft and air traffic control
systems. Since receiver autonomous integrity
monitoring (RAIM) is only partially effective against
this type of disruption (effectively a “signal
spoofing”), the pilot may not be aware of any
erroneous navigation indications; ATC may be the
only means available for identification of these
disruptions and detect unexpected aircraft position
while monitoring aircraft for IFR separation.


Pilots reporting potential interference should

identify the NAVAID (for example, VOR) malfunc-
tion or GNSS problem, location of the aircraft (that is,
latitude, longitude or bearing/distance from a
reference NAVAID), magnetic heading, altitude, date
and time of the observation, type of aircraft
(make/model/call sign), and description of the
condition observed, and the type of receivers in use
(that is, make/model/software revision). Reports
should be made in any of the following ways:


Immediately, by voice radio communication

to the controlling ATC facility or FSS.